feat: add swift implementation to lcci problem: No.16.02 (#2726)

* Swift Implementation for LCCI 16.02

* Update lcci/16.02.Words Frequency/README_EN.md

* Update lcci/16.02.Words Frequency/README.md

---------

Co-authored-by: thinkasany <480968828@qq.com>

Author: klever34

lcci/16.02.Words Frequency/README.md

@@ -203,6 +203,22 @@ WordsFrequency.prototype.get = function (word) {
  */
 ```
 
+```swift
+class WordsFrequency {
+    private var cnt: [String: Int] = [:]
+
+    init(_ book: [String]) {
+        for word in book {
+            cnt[word, default: 0] += 1
+        }
+    }
+
+    func get(_ word: String) -> Int {
+        return cnt[word, default: 0]
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- end -->

lcci/16.02.Words Frequency/README_EN.md

@@ -215,6 +215,22 @@ WordsFrequency.prototype.get = function (word) {
  */
 ```
 
+```swift
+class WordsFrequency {
+    private var cnt: [String: Int] = [:]
+
+    init(_ book: [String]) {
+        for word in book {
+            cnt[word, default: 0] += 1
+        }
+    }
+
+    func get(_ word: String) -> Int {
+        return cnt[word, default: 0]
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- end -->

lcci/16.02.Words Frequency/Solution.swift

@@ -0,0 +1,13 @@
+class WordsFrequency {
+    private var cnt: [String: Int] = [:]
+
+    init(_ book: [String]) {
+        for word in book {
+            cnt[word, default: 0] += 1
+        }
+    }
+
+    func get(_ word: String) -> Int {
+        return cnt[word, default: 0]
+    }
+}